Haemophilus influenzae, either type b or nontypable, are human pathogens and the cell surface lipooligosaccharide (LOS) of these organisms is an important factor in their ability to initiate disease. Understanding the structural model of these molecules is important to an understanding of their role in pathogenesis of human disease. Since these LOS's do not contain repeating O- antigen units, we will address the hypothesis that the antigenic heterogeneity of these LOS's is based on the complex interaction of the primary and tertiary structure of the oligosaccharides combined with an interaction with the lipid A moiety of the LOS. To define the model upon which this is based, the antigenic and physicochemical structure of these LOS's will be studied and related to the genes for LOS synthesis. This will be accomplished by the study of four H. influenzae strains, two which are nontypable and two which are type b. The LOS of these four strains have been shown to be antigenically heterogeneous in their specific and conserved regions. The model for the LOS from these strains will be defined by: 1) Developing a family of H. influenzae LOS mutants similar to the enterobacterial LPS mutants using bacteriophage selection and transposon mediated mutagenesis; 2) Mapping the epitope structure of the oligosaccharide portion of LOS parent and mutant LOS in order to define antigenic structure of the LOS; 3) Studying the role of LOS as a target for human bactericidal and opsonophagocytic antibody using human anti-LOS antibody and F(ab2)' fragments of anti-LOS monoclonal antibodies to attempt to block activity and determine LOS sites of bactericidal antibody action; and 4) Isolating the individual oligosaccharide chains of LOS from the study strains and their mutants and performing physicochemical analysis of the oligosaccharides to aid in the development of the model for H. influenzae LOS.